Right now, the mostly discussed way of sending any kind of Car-to-Infrastructure or Car-to-Car data out is a WiFi like standard Dedicated Short Range Communication (DSRC). Sending infrastructure data out over a cell phone network can be done today, but only by using unicast person-to-person (P2P) connections.
Predictive traffic light data is of interest to a larger group of vehicles within a certain geographic area. Per definition, broadcast is the technology of choice if the same data has to be send to many clients (unidirectional). DSRC has a short range. Although broadcast is supported in cell phone technology, many router implementations are blocked, and cell phone networks generally only support unicast. That means the amount of traffic is being multiplied with the number of listening clients. This makes it very expensive to scale a system up, e.g. experienced today by IP-TV providers. With IPv6 multicast/broadcast shall be supported, but today servers of e.g. www.espn360.com, which offer live streams, stream it in a point2multipoint fashion.
A Radio Data System (RDS), is commonly known, as a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts.
There exists broadcasting of traffic reports through the Radio Data System, which is generally used by motorists, to assist with route planning, and for the avoidance of traffic congestion. A receiver is used to receive the broad cast, and can be set to pay special attention for special broadcasts. For instance, the receiver will receive the broadcast and stop a current action being performed by the receiver and either play or retune to the traffic announcement.
There also exists a Traffic Message Channel (TMC), which is a technology for delivering traffic and travel information to drivers. It is generally digitally coded using a FM-RDS system on conventional FM radio broadcasts. The TMC is also be transmitted on DAB or satellite radio, as well. The TMC allows silent delivery of dynamic information suitable for reproduction or display in the language chosen by the user and without interrupting normal audio broadcast services. This data is then generally integrated directly into a navigation system unit, and gives the driver detailed information regarding pending traffic situation. The TMC allows the driver to take alternative routes to avoid the traffic issues.